The present invention pertains generally to devices and methods that are useful for inspecting and evaluating corneal donor tissue. More particularly, the present invention pertains to devices and methods that use optical techniques to evaluate both the material properties and the profile of corneal donor tissue in order to determine a composite optical structure of the donor cornea. The present invention is particularly, but not exclusively, useful for screening and selecting donor corneal tissue for the purpose of providing a suitable match for a particular transplant recipient.
In order to determine whether a particular donor cornea is suitable for use in a transplant surgical procedure, there are essentially two issues which need to be addressed. The first concerns whether the donor cornea has the requisite optical properties for use in a transplant procedure. Obviously, if the donor cornea is incapable of achieving the desired optical performance, it should be rejected. The second issue, which is not so obvious, concerns whether an optically acceptable donor cornea has a physical profile that is suitable for use with a particular patient. The issues of optical quality and profile suitability are both important for the screening and selection of an appropriate donor cornea.
Insofar as the optical quality of a donor cornea is concerned, it is known that various optical interference techniques, such as interference polarization, wavefront analysis, or spectral analysis, can be useful for determining specific material properties of the cornea that will affect its optical quality. For example, it is known that optical interference techniques can be used to detect and identify inhomogeneities which may be caused by such tissue characteristics as density, amorphousness, crystallinity and transparency. Further, these interference techniques can also be used to detect residual tissue damage such as corneal scarring and stromal disease. Still further, they can be used to collect information concerning stress and anisotropy. As indicated above, a knowledge of these material properties of a donor cornea is of great importance to the vision healthcare provider. As also indicated above, however, for a more complete evaluation of a donor cornea it is also necessary to consider information about the physical profile of the donor cornea.
In addition to a thorough knowledge of the optical properties of a donor cornea, complete and accurate information on the dimensional profile of a donor cornea can be of great value to the healthcare professional who is performing a surgical transplant procedure. Not only does dimensional information permit a more suitable match between the donor and the recipient, it also allows for better control of tissue interface during surgery. Further, dimensional compatibility between donor and recipient can lead to a more effective surgical outcome with better patient response and shorter recovery time.
In light of the above it is an object of the present invention to provide a system and a method for evaluating a donor cornea which provides information concerning the optical properties of the cornea, as well as the physical profile of the cornea. It is another object of the present invention to provide a system and a method for evaluating a donor cornea which uses optical techniques to measure and evaluate both physical and optical properties of a donor cornea. Yet another object of the present invention is to provide a system and a method for evaluating a donor cornea which allows the donor cornea to remain inside the protective confines of a containment vessel during examination. Still another object of the present invention is to provide a system and a method for evaluating a donor cornea which is easy to use, relatively simple to implement, and comparatively cost effective.
A system for evaluating a donor cornea in accordance with the present invention includes a light source that will generate a light beam having a predetermined characteristic and a selected configuration. Specifically, insofar as the light beam characteristics are concerned, the light from the light source can be collimated light for use in a wavefront analysis, it can be white light for use in a spectral analysis, or it can be polarized light for use in a polarization analysis. Insofar as light beam configurations are concerned, the light beam can have a generally circular cross-section so that the light will simultaneously illuminate an entire donor cornea, or it can have a slit configuration so that only a relatively narrow strip of the donor cornea will be illuminated.
As intended for the device of the present invention, when the light beam is in its circular cross-section configuration, the light is directed along a path through the donor cornea to a detector. More specifically, this path will be generally aligned with the optical axis of the donor cornea. For a circular cross-section light beam configuration, the entire donor cornea will be illuminated. The detector can then evaluate the light that is transmitted through the donor cornea, including the endothelium, to identify changes in the characteristics of the light (e.g. phase shift, spectral shift, or polarization changes). In turn, these changes can be used to evaluate the optical aberrations that are introduced by the donor cornea. Based on this evaluation, the optical properties of the donor cornea are determined in a manner well known in the art.
Regardless of the particular characteristics chosen for the light beam that is used to determine the optical properties of the donor cornea, when the light beam is switched to its slit configuration, some of the light will be scattered off-axis by the donor cornea. This scattered light can then be collected by another detector and used to measure dimensions for a profile of the donor cornea. For example, these dimensions can include a thickness, an arc length, and a chord length for the donor cornea.
In addition to the optical elements for the present invention set forth above, the device of the present invention can also include a cell for holding the donor cornea. An example of such a cell is disclosed in co-pending U.S. patent application Ser. No. 09/464,110, for an invention entitled xe2x80x9cOptical Donor Tissue Cellxe2x80x9d, which is assigned to the same assignee as the present invention. The present device can also include a mount that has a stage for holding the cell. Additionally, the cell can be rotated with the stage to move the donor cornea relative to the light source, or the scattered light detector can be moved relative to the donor cornea in the cell. Either way, different slits of the donor cornea can be illuminated for subsequent analysis and use in establishing a profile for the donor cornea.
In the operation of the present invention, the light beam from the light source is directed along an initial path toward the donor cornea. Before the light beam reaches the donor cornea, the particular desired characteristic for the light beam is established. Specifically, the light can be collimated, polarized, sheared or otherwise defined. Additionally, a switching means is provided for selectively alternating the light beam between its first configuration, wherein the light beam is dimensioned to illuminate the entire cornea, and its second configuration wherein the light beam is dimensioned to illuminate only a slit of the donor cornea.
When the light beam is in its first configuration to illuminate the entire cornea, the light that is transmitted through the donor cornea is evaluated to determine the optical characteristics of the donor cornea. Depending on the characteristic of the light beam, this evaluation can be done either by wavefront analysis, spectral analysis, or polarization analysis to provide information on such material qualities of the donor cornea as tissue strain, tissue stress, temperature degradation, extracorporeal aging, and damage. When the light beam is in its second configuration, for slit illumination of the donor cornea, scattered light from the illuminated slit can be used to determine anterior and posterior edges of the corneal specimen (donor cornea). Also, radii of curvature information and elevation data, as well as corneal thickness and chord length can be determined.
A computer for collating data collected by the detectors is then used to prepare an evaluation report of the donor cornea. As specifically intended for the present invention, this evaluation report will include information on both the optical qualities and the dimensional profile of the donor specimen. Accordingly, the evaluation report is useful for screening and selecting an appropriate specimen for a recipient, and for use in planning a surgical transplant procedure.